Restricted Growth of Polyvinyl Alcohol Crystalline Regions Within a Flexible Network for Visual Stress Perception

ABSTRACT Polyvinyl alcohol exhibits excellent biocompatibility, and its mechanical strength can be significantly enhanced through freeze‐thaw cycles and salting‐out methods. However, excessive uncontrolled crystalline growth under both strategies causes significant light scattering, making pure polyvinyl alcohol gels unsuitable for sensitive birefringence under stress and strain. This study introduces restricted flexible polyacrylamide networks into polyvinyl alcohol system to suppress excessive polyvinyl alcohol molecular aggregation through controllable polyacrylamide regulation. The crystalline size of polyvinyl alcohol molecules can be controllably increased through the freeze‐thaw and salting‐out processes, balancing the trade‐off between gel crystallinity and transmittance. A flexible gel exhibiting high birefringence sensitivity under mechanical deformation was achieved without incorporating anisotropic nanofillers, offering a novel route for visual stress perception. Leveraging the high sensitivity to birefringence, visual polarized light responses under multi‐point strain in the torso allow efficient evaluation of relaxation, effective, and ineffective training. Utilizing the Hofmeister effect‐induced salting‐in and salting‐out mechanism, complex shapes and multi‐dimensional structures were tailored for plasticity‐recovery customization through the competitive interaction between the shaping component (polyvinyl alcohol) and the elastic component (polyacrylamide). This flexible strategy enriches the customizable design of gel materials and holds great potential for applications in health monitoring, early‐warning systems, anti‐counterfeiting encryption, and biomimetic design.